1. Field of the Invention
The invention relates to video de-interlacingand more particularly to an video de-interlacing method considering luminance difference vectors adjacent to an interpolated pixel.
2. Description of the Related Art
Progressive display devices display complete frame every refresh. In contrast, interlaced signal, such as NTSC and PAL, typically display even and odd field interlacing. To display interlaced signal on a progressive display device, video rendering systems have to generate pixel data for scan lines that are not received in time for the subsequent field update. This interlace-to-progressive conversion process is referred to as de-interlacing. Current de-interlacing methods comprise intra-field de-interlacing, motion adaptive de-interlacing, and motion compensation deinterlaceing. The intra-field de-interlacing uses a single field to reconstruct one progressive frame. Presently, Directional edge interpolation, also known as edge dependent interpolation (EDI) or edge-based line average (ELA) method, is the most popular algorithm in the intra-field de-interlacing domain.
FIG. 1 illustrates directional edge interpolation using a 5×3 window. An interlaced Line LI includes interpolated pixels with unknown luminance requiring interpolation with known luminance of two candidate pixels selected from an upper line LU and lower line LL. If F is a current interpolated pixel with unknown luminance l(F) to be interpolated with luminance of pixels selected from candidate pixels A to E and G to K, then D1, D2, D3, D4, and D5, respectively associated with directions  and  represent directional differences around the current interpolated pixel F, defined as:D1=|l(A)−l(K)|D2=|l(B)−l(J)|D3=|l(C)−l(I)|,D4=|l(D)−l(H)|D5=|l(E)−l(G)|where l(pixel name) denotes luminance of a pixel with the pixel name.
ELA uses the direction associated with the smallest difference Ds as the direction with highest correlation, where Ds is defined as:Ds=min(D1,D2,D3,D4,D5).Since pixels on the direction associated with the smallest difference Ds are strongly correlated, the luminance l(F) of the current interpolated pixel F is approximated by interpolation of adjacent pixels on the direction. That is,
      l    ⁡          (      F      )        =      {                                                                      (                                                      l                    ⁡                                          (                      A                      )                                                        +                                      l                    ⁡                                          (                      K                      )                                                                      )                            /              2                                                                          if                ⁢                                                                  ⁢                                  D                  s                                            =                              D                1                                                                                                        (                                                      l                    ⁡                                          (                      B                      )                                                        +                                      l                    ⁡                                          (                      J                      )                                                                      )                            /              2                                                                          if                ⁢                                                                  ⁢                                  D                  s                                            =                              D                2                                                                                                        (                                                      l                    ⁡                                          (                      C                      )                                                        +                                      l                    ⁡                                          (                      I                      )                                                                      )                            /              2                                                                          if                ⁢                                                                  ⁢                                  D                  s                                            =                              D                3                                                                                                        (                                                      l                    ⁡                                          (                      D                      )                                                        +                                      l                    ⁡                                          (                      H                      )                                                                      )                            /              2                                                                          if                ⁢                                                                  ⁢                                  D                  s                                            =                              D                4                                                                                                        (                                                      l                    ⁡                                          (                      E                      )                                                        +                                      l                    ⁡                                          (                      G                      )                                                                      )                            /              2                                                                          if                ⁢                                                                  ⁢                                  D                  s                                            =                              D                5                                                        ,      where l(A) to l(K) denotes luminance of pixels A to K.
The ELA algorithm provides acceptable performance in many cases. However, an ambiguous case as shown in FIGS. 2A and 2B may occur. FIG. 2A shows an original image composing lines LU, LI and LL with luminance of each pixel shown by a number. FIG. 2B shows an interlaced image with line LI missed. ELA uses directions  or  as the direction with highest correlation since the directional differences thereof are all |100−100|=0. However, the direction  is the correct interpolation direction even though the directional difference thereof is |65−67|=2, greater than 0.